Satyr

A satyr was lifeform that could be found on the planetMegas-Tu. It had horns that, along with its lower body, looked like those of an animal, although it also had a recognizably humanoid face, chest, arms, and neck.

In the script of "The Magicks of Megas-Tu", this being is twice referred to, both times as a "little boy satyr." The script includes some actions that were written for the child satyr but which are not shown in the episode's final version. Specifically, the teleplay states, "[He] smiles up at Lucien, waves, then picks up his toy, hurries off."

The Japanese name for the episode "The Magicks of Megas-Tu" references this type of lifeform; the title, translated back into English, is "The Satyr on the Magic Star Megas-Tu". (Star Trek Concordance, 2nd ed., p. 84)